This invention relates generally to permanent magnets and, more particularly, to configurations of permanent magnets used to produce a magnetic field at a specified situs having a required strength and flux alignment. This application is related to U.S. Pat. No. 4,875,486 entitled "Instrument For Non-Invasive Testing For Glucose And Other Body Fluid Constituents".
The use of permanent magnets to produce and maintain magnetic fields of predetermined characteristics has found wide-spread application throughout varied areas of technology. As one example, the use of permanent magnets in loud speakers makes possible the accurate reproduction of sounds and music.
Permanent magnets offer numerous advantages over electromagnets, the most prominent of which is the production and maintenance of a magnetic field without requiring the application of electrical energy, thus producing a device which is independent of the need for an external power source. This is an important consideration in designing portable apparatuses, and also results in constructions requiring little or no maintenance beyond initial assembly.
The present invention utilizes particular arrangements and configurations of permanent magnets to create strong, uniform magnetic fields. Although the uses to which the present invention may be put are described herein as principally in connection with medical diagnostic equipment, it should be understood that the invention may be utilized wherever a magnetic field is required.
As described in the above-mentioned co-pending patent application, the use of a magnetic field makes possible the non-invasive testing of human body systems to detect the presence of certain substances. In particular, permanent magnets are used to create a first, or biasing magnetic field within which initially randomly oriented .sup.1 H protons present in the nuclei of the substance being tested are aligned. Thereafter, a second energy field is applied to increase the energy level of said nuclei. When the second energy field is allowed to collapse, the nuclei return to their original, aligned state, releasing energy which is detected and analyzed in the form of an image or a spectrum. Certain spectra have been found to be characteristic of particular substances, and the technique of nuclear magnetic resonance (NMR) may be used to establish the presence and identity of such substances and the concentrations within which such substances are present.
Heretofore, the use of NMR has called for the construction of large, expensive machinery to produce and maintain the magnetic fields necessary for such testing. In utilizing NMR diagnostic techniques, creating and maintaining the primary or first magnetic field is of critical importance. It has been found that in designing such equipment to be compact and portable, it is necessary to create a primary magnetic field which is uniform in strength, and which has a relatively dense magnetic flux. Visually, such a field may be defined by the lines of flux which indicate not only the strength of the magnetic field, but its orientation as well.
Ideally, the lines of flux should be parallel or nearly parallel and uniformly spaced throughout the test zone, i.e., that portion of the magnetic field used for diagnostic purposes. It has been found it efficacious to produce the first or primary magnetic field with permanent magnets rather than electromagnets.
The use of magnets and magnetic energy to diagnose and treat biological disfunctions is well known. As an example, in French Patent No. 2,562,785 (Jeandey, et al.) a permanent magnet system for NMR imaging medical diagnostics uses pole pieces separated by stacked permanent magnets to form an open examination area with the pole pieces "bridging" both stacks of magnets. Jeandey, et al. also teach the use of electromagnetic coils to adjust the resulting magnetic field.
Japanese Patent No. 56-14145 (Nippon Denshi K.K.) teaches an arrangement of permanent magnets held within a cylinder. A spacer is placed within the cylinder and sandwiched about the spacer are a pair of cylindrical pole pieces. The entire assembly is held together by placing magnets outside the pole pieces (separated from the pole pieces by a buffer) and utilizing the attraction of the magnets for each other to hold the entire assembly in place. Nippon Denshi also apparently teaches the use of pole pieces having raised central portions, that is, flat faces which extend into the air gap between the pole pieces and from which the operative flux apparently emanates. Nippon Denshi fails to teach any use of auxiliary magnets in combination with the principal magnets.
U.S. Pat. No. 4,635,643 (Brown) teaches the use of NMR equipment to perform in vivo measurement of the mineral content of bone. Brown, however, teaches no arrangement of permanent magnets in constructing a test chamber for NMR use.
In U.S. Pat. No. 4,134,395 (Davis) the patentee teaches the use of a permanent magnet to detect diseased body parts by observing the effect the application of that magnetic field has on the muscles of the legs. Davis also describes the physical characteristics of a bar magnet showing the extent and shape of the magnetic field produced by such a magnet.
U.S. Pat. No. 3,467,076 (Frisch, et al.) discloses a magnet arrangement used to produce a field of high magnetic flux within which the effect of magnetic energy on living things may be observed. Frisch, et al., use a centrally-located electromagnet sandwiched between ferromagnetic pole pieces which extend beyond the edges of electromagnet to form an air gap within which the magnetic flux is produced.
In U.S. Pat. No. 3,358,676 (Frei, et al.), a method of treatment is taught which requires the use of an extremely large and cumbersome magnet structure.
The size and complexity of magnets required to utilize the phenomenon of NMR in making diagnoses is exemplified in an article appearing in the December, 1977 issue of Popular Science magazine, entitled "Damadian's Supermagnet". The author discusses the use of NMR to detect cancer cells: the size and strength of the magnetic field required to perform this diagnostic technique, and the size and complexity of the magnet used to produce such a field are well described.